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Thread: E39 ASC+T Light Question; testing clarifications

  1. #1
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    E39 ASC+T Light Question; testing clarifications

    2001 BMW 525i M54b25

    I have googled this quite a bit, and maybe Im keying the wrong words, but I havent found much for the ASC+T light (triangle with the circle). Every thread is with the 'trifecta' of the ASC, ABS, and Brake light. Sincerely I apologize for this

    I want to go as far down the testing tree as I can without sending the car off to the mechanic or sending the ABS module in. This is my daily and the car is serviceable as it is today.


    A few notes:
    • Only the ASC light is on; ABS and Brake light are NOT.
    • ABS module has a repair sticker so I can assume this was repaired by the PO; unknown miles, however. Car has 150k miles today.
    • Wheel speed sensor wires pass visual tests, but I can try cleaning them.
    • ASC light turns on as soon as the car turns on
    • No codes are present from OBD2 scanner, no SES light
    • No other indications of fault. Speedometer, etc etc etc all working fine. "All systems nominal"


    I am reading Bluebee's thread on how to diagnose ABS trifecta and I am sorta lost on a few steps...
    First, how relevant is this for me since I dont have the trifecta? Will I be able to diagnose?
    So, Im sorta lost on the steps, starting at 1...

    Test 1: Switch the DMM into the diode test position
    I'm assuming this is the continuity test? My multimeter beeps when there is continuity (ends touch). I didnt get any beeps at any of the configurations for the pins.
    So is this a pass?

    TEST 2: Switch the DMM into resistance checking mode (optional)
    I switched my voltmeter to 2000K (2M?) and I didnt quite get the numbers that Bluebee got 7.5 / 4.4 (depending on orientation) and I was getting much less, 700-900 @ 2000K, which I assume is .7 to .9 @ 2M. So not a lot of resistance here...

    I didnt do Test 3 & 4 which require spinning the wheel because its just me...


    So a few questions....
    1. Are these tests relevant to me?
    2. Which tests would be tell-tale?
    3. Should I just try and get a scanner or go to a mechanic for a BMW scan?


    From my googling I did hear some folks say there is some sort of actuator at the intake that swings open at the start and closes again. though I *think* this is for early E39. Not my late? I cant see or hear any sort of device on my car.
    Ive also read a throttle cable can be loose, but I again I think this is Early E39 problems, not late.

    Otherwise I havent read much that is relevant to me, but I could be misreading.

    I really dont wanna go right to sending the ABS module away when it could be a wheel sensor or otherwise.

  2. #2
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    Others, I'm sure, can offer more in depth advice than me. But it sounds like your scanner isn't capable of reading codes other than engine codes. Get it read by a better scanner. Start with that - rather than chasing your tail around and doing endless searches on the internet. There WILL be a code. Knowing the code won't necessarily tell you exactly what has failed, but it will get you heading in the right direction. Write any/all codes down that you find, then clear it. See if anything comes back. Then post your results - that will likely be much more helpful to others.

    I thought the Triangle light was primarily about transmission problems?

    Is the car in limp mode?

  3. #3
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    The car isn't in limp mode but I've been there before long ago.. (dirty neutral position switch)

    To be honest I thought it was a general indicator to state my wiper fluid was low but I opened the manual and it said it was for ASC+T

  4. #4
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    Quote Originally Posted by jaredmac11 View Post
    To be honest I thought it was a general indicator to state my wiper fluid was low but I opened the manual and it said it was for ASC+T
    Is that some sarcasm, there?

    The reason I mentioned it was because I wasn't aware (and I could be wrong... hence the ? above) that the triangle had anything, directly, to do with the brakes/ABS. Meaning, if ONLY the triangle was lit, it was primarily a tranny/tranny sensor issue.

  5. #5
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    Only a bit, just what I tell myself to keep my head in the sand. Since you brought it up, I reminded myself I had that light come up when I went in to limp mode and it also threw a CEL which pointed me to a neutral position switch. But that was awhile back and I went to the manual to remind myself what it referred to and it said ASC/DSC? I'll go back once more.

    Sent from my LG-H830 using Tapatalk

  6. #6
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    Borrow or buy a code reader that has the capacity to check live data for ABS/Traction control. And in the ABS sub menu you can display the wheel speed sensors.

  7. #7
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    OK, now I feel a little like an idiot. I don't know what I was thinking. OF COURSE the triangle deals with traction control! That's why it lights up when I turn 'off' traction control to have some fun in the corners! How I forgot that, I dunno. Sorry about that. But, yes, read it with the appropriate code reader as a good first step. There are ways to check speed sensors, as well, with a DMM - check the DIY section. But, that triangle can come on for tranny related issues, as well - I currently have that going on (sporadically).
    Last edited by DennisG01; 03-26-2019 at 12:58 PM.

  8. #8
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    1999 5281
    the triangle (DSC) light can also come on with engine management issues. yes a BMW specific code reader is a must when diagnosing outside the OBDII protocol parameters, basically anything but the engine codes. if im not mistaken, your model has DSC, not ASC or ASC+t, it should always be enabled when the engine is started, the switch must be manually depressed to turn it off, if the light is on at startup, there should be a fault code.

  9. #9
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    Quick update. I didnt do any diag myself. Took it to my indy and he determined it was likely the steering wheel angle sensor since that was the only relevant code. I just dont think its a complete fault since my guess is its still sending out some sort of signal or whatever. Also he cleared codes and it hasnt popped back up yet.

    The indy shop wont let me pick up a part, install it, and then have them code it. Maybe I can find someone who can, but until then I'll have to run without DSC for a minute. I just hate having lights on my dash.

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